Prediction and control of residence time of an object or particle in a reactor, heat exchanger or holding tube is important for many continuous flow processing operations. One example of a continuous flow processing operation is aseptic processing of liquid based foods, such as potato soup. Usually, liquid based foods include liquid particles, large solid particles and smaller solid particles. The prediction and control a particle""s residence time assures the correct processing time for the particle. The residence time of large solid particles is especially important during the aseptic processing of foods with large solid particles. Continuous flow operations usually involve a flow confined by at least one wall. Hence, the flow of particles may be slower near the wall than away from the wall. In fact in a tube with laminar flow, the outside portion of the flow is usually much slower than the center portion of the flow. This creates a situation where individual particles of the flow can be under-processed or over-processed, due to the different residence times.
Conventional continuous flow reactors, heat exchangers, and holding tubes have relatively wide distributions of residence times for individual particles of the flow. The individual particles can have much longer or shorter processing time than the average processing time of all the particles. A wide distribution of residence times means some particles are processed for much shorter times, while other particles are processed for much longer times. To compensate, often the processing time is increased to insure that the fastest moving particles receive the minimum allowable processing. Whereby, the tradeoff is that the slowest moving particles are over-processed. Depending on the application, this can translate to inferior quality product, increased energy usage and reduced throughput.
Several approaches have been used to resolve the problems associated with the wide distribution of residence times in continuous processing. A first approach is the use of empirical data or mathematical models to determine the distribution of residence times for a particular set of flow conditions of individual particles. Once the distribution is determined, the processing time can be adjusted appropriately. The problem is that accurately modeling the residence time is a complex process because of the interaction of numerous factors. Likewise, the collection of empirical data is difficult because seemingly insignificant, uncontrolled differences in flow conditions can result in important changes of residence time distribution. A second approach is to control flow parameters such as laminar or turbulent flow, tube diameter, tube length, or flow path to create the desired distribution of residence times. The control of flow parameters to achieve the desired distribution of residence times is problematic for the same reasons as the first approach. Furthermore, even if residence time can be accurately predicted or measured, the fact remains that the distribution is often wider than desired and flow parameter control is often inadequate to achieve a narrow distribution of residence times. A third approach is to use batch processing rather than continuous processing. Batch processing can easily provide a narrow distribution of residence times and is often the best solution. The problems with batch processing is that it creates materials handling problems, scheduling problems and is more expensive. A final approach is the development of mechanisms that physically control residence time. Current applications of this approach are not without disadvantages. Some are difficult to implement, some damage particles of the flow, while others do not always provide a uniform control of residence time. Furthermore, they do not specifically control residence time of liquid particles apart from solid particles in the flow. This leads to the over-processing of some of the particles in the flow, thereby resulting in a reduction in product quality.
It is an object of the present invention to provide a system for the uniform processing of a flow of particles.
It is an object of the present invention to provide the control of residence time of individual particles in a continuous flow processing operation.
It is an object of the present invention to provide system to prevent the necessity of over-processing foods to meet safety requirements in a continuous flow processing operation.
The present invention provides a segmented flow device for controlling the residence time of particles in a flow. The device includes a processing conduit having an inlet end and an outlet end. A feed port is at the inlet end for inserting the flow to be processed. A release port is at the outlet end for removing the flow after processing. The device includes a series of barriers moving through the processing conduit to segment the flow during processing to allow control of residence time of the particles of the flow. A continuation section provides a path between the inlet and outlet ends of the processing conduit for receiving the barriers from the outlet end and returning the barriers to the inlet end. A first input in the device is for providing an inlet pressure to the inlet end and a second input for providing an outlet pressure to the outlet end, such that the inlet and outlet pressures are also used for controlling the flow.